1. Field of the Invention
The present invention relates to a black color generation amount determining method in black printing, a black color generation amount determining apparatus in black printing and a media having recorded thereon a black color generation amount determining program in black printing.
2. Description of the Prior Arts
Various methods have conventionally been proposed for determining a black color component in performing black printing, one of which is proposed in xe2x80x9cTheory and Practice of Black Printerxe2x80x9d at Electrostatic Society Magazine, Vol. 3, No. 3, pp.67 to 75.
The basic idea of black printing is such that an undercolor amount which is a common minimum component is obtained based upon tone data of so-called CMY (cyan, magenta, yellow) to calculate K (black) component by multiplying the undercolor amount by a constant number called a black generation ratio (BGR), while a predetermined ratio (UCR ratio) is multiplied to the K component in order to replace the CMY component with the K component for attaining decreased amount.
On the other hand, Japanese Laid-Open Patent Application No. HEI 7-87347 discloses a method for determining an UCR ratio based upon chroma upon performing such black printing.
Black printing is put to practical use in a color printer connected to a computer, wherein K dot is marked with CMY dot.
The principal objective in the above-mentioned conventional method for determining a black color component is how to prevent color difference from being generated. A remarkableness of dot is liable to become a problem above the color difference as to a device having a relatively large dot diameter such as a color printer. On the other hand, there may frequently be the case where colors are different from one another even if they have the same undercolor amount. It has been known that the remarkableness of each K dot is different, when these different colors are printed by the color printer.
An object of the present invention is to provide a black color generation amount determining method in black printing capable of making K dot unremarkable including a color printer.
The black color generation amount determining method in black printing according to the present invention is constructed such that, upon generating a black color component in order to perform black printing in a color space for printing comprising a plurality of approximately equivalent element colors, the black color component is caused to be generated to have a predetermined relationship with respect to a gray component in the plurality of element colors, and that the brighter a color is, the more the generation amount decreases.
In the present invention having the aforesaid construction, the black color component is caused to be generated to have a predetermined relationship with respect to the gray component in the plurality of element colors upon performing black printing in the color space for printing comprising the plurality of approximately equivalent element colors. The generation amount of the black color component varies not only in accordance with the gray component, but also in relation to brightness of data before conversion, that is, the brighter the data before conversion is, the less the black color component generates. Accordingly, the generation amount of the black color component is decreased in the brighter color even if the gray component is the same, thereby making the black color component unremarkable.
Therefore, the present invention can provide the black color generation amount determining method capable of making dot unremarkable, since the present invention places great importance on not only the viewpoint of the color difference but also the viewpoint of the remarkableness of dot in black printing to control the generation amount of the black color component with respect to a bright color.
Various deciding methods can be adopted to the gray component which is the basis for generating the black color component. Another object of the present invention is to provide a more specific deciding method of the gray component.
In the black color amount determining method in black printing according to the present invention, the gray component is decided based upon an undercolor amount which is a common minimum component in the plurality of element colors.
In the present invention having the aforesaid construction, the gray component is decided based upon the obtained undercolor amount which is the common minimum component in the plurality of element colors. The undercolor amount in a narrow sense corresponds to minimum tone data if, for example, the plurality of element colors are expressed by CMY and the undercolor amount is afforded as the tone data representing the densities of CMY. However, the undercolor amount is not limited to the one in a narrow sense. For example, there has been known a method as an undercolor removal in which the undercolor amount obtained in this way is simply replaced with the black color component for subtracting the component value of each element color by the replaced value. In this case, the element color of the minimum component value is originally not utilized at all. However, it has been know that chroma is decreased in the aforesaid method. Therefore, a method of an undercolor addition may actually be performed to add a predetermined component amount to each of the element colors after subtracting the undercolor amount. Accordingly, an experiential compensation may be added to the undercolor amount, so that the undercolor amount which is the common minimum component in the plurality of element colors is merely used as the basis of the gray component. The present invention includes the undercolor amount suitably increased or decreased.
In this way, the present invention can provide the black color generating amount determining method capable of deciding the gray component in a relatively simple manner.
It should be noted that the method of the undercolor removal or undercolor addition may be adopted in the present invention. In this case, the undercolor removal amount can be varied related to unfixed generation amount of the black color component. For example, upon generating the black color component while determining the undercolor removal amount for subtracting the component amount of each element color based upon the undercolor amount, the undercolor removal amount may be determined to be great as the generation amount of the black color component increases. In such a construction, the undercolor removal amount varies with the variation of the actual generation ratio of the black color component since the generation ratio of the black color component varies in accordance with brightness, whereby the balance as the undercolor amount is maintained.
Brightness of a color is the basis for determining the generation amount of the black color component. The tendency may show that the brighter the color is, the more the generation amount decreases. Therefore, the basis can include the other factors than brightness.
Therefore, further object of the present invention is to provide a black color generation amount determining method in black printing capable of having a basis including other factors than brightness.
The black color generation amount determining method in black printing according to the present invention has the construction for deciding by adding chroma as a guideline of bright color to brightness.
In the present invention having such a construction, the greater chroma is, the greater the index of brightness is by adding chroma to the index of brightness, with the result that the generation amount decreases. On the other hand, the smaller chroma is, the smaller the index of brightness becomes, so that the generation amount increases. When this construction is adopted, the generation amount of the black color component increases in the portion of nearly gray having low chroma, while it decreases in a bright portion.
Therefore, according to the present invention, the generation amount of the black color component increases in the portion of nearly gray having low chroma, so that the gray balance is easy to be kept, while the generation amount of the black color component is controlled in the bright area by increasing the index of brightness, so that the black dot becomes unremarkable.
When the generation amount of the black color component is calculated based upon brightness, it is necessary to obtain brightness as the assumption. If the objective color space possesses a parameter of brightness as the direct element, this parameter can be used. However, on the assumption of the color space for printing comprising a plurality of approximately equivalent element colors, the parameter of brightness as the direct element is not be provided.
Therefore, further object of the present invention is to provide a suitable black color generation amount determining method in black printing adopting to the case of not providing a parameter of brightness as the direct element.
The black color generation amount determining method in black printing according to the present invention obtains brightness of color with reference to a table on which a corresponding relationship is recorded in advance.
In the present invention having such a construction, the table is prepared on which each brightness of each color is recorded, whereby the generation amount of the black color component is determined as described above by obtaining brightness with reference to the table.
Accordingly, brightness can accurately and simply be obtained by referring the table for brightness of color.
Although the table referred to in this case may be the one capable of referring at least for brightness, the table may be referred to for the other parameters such as chroma in addition to brightness. This table may always be kept, or may be present only when the generation amount of the black color component is determined. Further, this table may be provided with a corresponding relationship among all colors of the data before conversion, or may be provided with a corresponding relationship for some colors. The corresponding relationship may be calculated by an interpolation calculation with respect to colors whose corresponding relationship is not recorded on the table. Further, accessing an external data base only in case of necessity is naturally included.
The Neugebauer equation is well-known for a reproducibility of colors by printing. Although it is generally difficult to realize due to a large calculation amount, the reproducibility of color can accurately be simulated if the calculation is possible.
Accordingly, further object of the present invention is to provide a black color generation amount determining method in black printing suitable for high calculation ability.
The black color generation amount determining method in black printing according to the present invention has the construction such that three stimulus values are obtained based upon the Neugebauer equation, whereupon brightness of color is obtained by performing a linear conversion of the three stimulus values.
In the present invention having such a construction, so-called three stimulus values can be obtained based upon the Neugebauer equation even if high calculation ability is required, whereby brightness can be obtained by the linear conversion if the three stimulus values are obtained.
Therefore, brightness can be obtained only by the calculation according to the present invention.
Black printing is performed in a printing stage. However, the image processing or the like is not always executed in the color space in the printing stage. Accordingly, an operation is frequently performed for color-converting the color space in the image processing into the color space in the printing stage.
Therefore, further object of the present invention is to provide a black color generating amount determining method in black printing suitably used upon the operation of the color-conversion from the color space in the image processing into the color space in the printing stage.
The black color generating amount determining method in black printing according to the present invention has the construction such that the generation amount of the black color component in the color space for printing is determined based upon the color data comprising a coordinate value of the color space different from that for printing.
In the present invention having such a construction, when the color space for printing is CMY, the color data represented by the coordinate value from the color space different from that of CMY, such as RGB (red, green, blue) or L*a*b* is used as a parameter to determine the generation amount of the black color component in the color space for printing including the black color component.
Therefore, most preferable generation amount of the black color component can be determined based upon the color data of the color space different from that for printing according to the present invention.
Although it is possible in this way to execute the determination of the generation amount of the black color component every time the printing operation is performed, it is enough to execute once the determination of the generation amount of the black color component to determine the black color component with respect to each color.
Therefore, further object of the present invention is to provide a black color generating amount determining method in black printing capable of decreasing the number of the determining operation of the black color component.
The black color generating amount determining method in black printing is utilized upon determining the black color component of the color conversion table used for color-converting from the color space different from that for printing into the color space for printing.
In the present invention having such a construction, once such a color conversion table is formed, the same color conversion table may be referred to for performing the color conversion upon the printing operation from the other color space.
Therefore, according to the present invention, the black color component whose dot is unremarkable is used for forming the color conversion table, so that the same table can be reused to decrease the operation number.
The black color generation amount determining method includes the case wherein the method is independently executed in an apparatus or the case wherein the method is incorporated in other apparatus to be executed as one function of the apparatus. In other words, the concept of the invention includes various embodiments. Accordingly, it is possible to be realized not only in a hardware but also in a software.
Therefore, further object of the present invention is to provide a black color generation amount determining apparatus as a hardware for realizing the concept of the present invention as the hardware.
The black color generation amount determining apparatus according to the present invention is the one for determining the generation amount of the black color component in order to perform black printing in a color space for printing comprising a plurality of approximately equivalent element colors, wherein the black color component is caused to be generated to have a predetermined relationship with respect to a gray component in the plurality of element colors, and the brighter a color is, the more the generation amount decreases.
Therefore, the present invention is capable of providing the black color generation amount determining apparatus affording the same effect.
Further, in case where the embodying example of the concept of the invention is a software for determining the generation amount of the black color component, it is ought to say that the present invention is naturally present on a recording media having the software recorded thereon to be utilized.
Accordingly, further object of the present invention is to provide a software for determining the generation amount of the black color component.
A media having recorded thereon the black color generation amount determining program according to the present invention is the one having recorded thereon the black color generation amount determining program for determining by a computer the generation amount of the black color component in order to perform black printing in a color space for printing comprising a plurality of approximately equivalent element colors, wherein the black color component is caused to be generated to have a predetermined relationship with respect to a gray component in the plurality of element colors, and the brighter a color is, the more the generation amount decreases.
Therefore, the present invention is capable of providing the media having recorded thereon the black color generation amount determining program in black printing.
The recording media may be a semiconductor chip, a magnetic recording media or optically magnetic recording media. This concept can be adopted to any recording media developed from now on in the same manner. There is no inquiring that the same concept is adopted to a reproducing stage such as a primary reproduction product or secondary reproduction product. In addition, the present invention is similarly utilized in the case of using a communication line as a supplying method.
Additionally, the concept of the invention is not so different when the invention is realized in partly the software and partly the hardware. Moreover, it may include an embodiment in which a portion of the program of the invention is recorded on the recording media which is read as the need arises.
The effect of rendering dot unremarkable as described above is demonstrated upon printing based upon the black color component determined in this way, whereby it should be said that the concept of the invention is effective for the color conversion table for printing used upon printing as well as is effective for the method or the apparatus for forming the color conversion table for printing. In this case, various types can be adopted for the format as the color conversion table or referring method. It is unnecessary for the table to always be usably developed. The table may be developed only when used. Further, the table may be distributed in a common condition and rendered suitable corresponding to an adopting system when installed. Additionally, although there may be the case where the color conversion table for printing is not always used in the printing stage, it is possible in this case to vary the generation amount of the black color component by using brightness as the index.